Conical scanning rotatable dielectric wedge lens which is dynamically balanced



June 7, 1966 c. E. OLCOTT 3,255,451

CONICAL SCANNING ROTATABL IELECTRIC WEDGE LENS WHICH IS DYNAMICALLY BALANCED Filed Jan. 2, 1963 2 Sheets-Sheet 1 Fm. Z.

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.r CHARLES E. WOLCOTT INVENTOR.

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GONIGAL SCANNING R T TA L DIELECTRI EDGE LENS WHICH IS NAMICALLY BALANC Filed Jan. 2, 1963 2 Sheets-Sheet 2 CHARLES E. W OTT INVENT ATTORNEYS United States Patent CONICAL SCANNING ROTATABLE DIELECTRIC WEDGE LENS WHICH IS DYNAMICALLY BAL- ANCED Charles E. Wolcott, El Cajon, Calif., assignor to Whittaker Corporation, a corporation of California Filed Jan. 2, 1963, Ser. No. 249,010 Claims. (Cl. 343753) This invention relates to an antenna for very high frequency electrical signals and more particularly relates to an antenna using a rotating dielectric wedge lens for use in conical scanning systems.

Very high frequency and microwave transmitting and receiving antenna systems often use a method of conical scanning for tracking. To develop the tracking function, the cylindrical main lobe of energy emanating from a feed is displaced from the line axis of the feed at a predetermined angle. This angular lobe is moved around the line axis at an angular velocity so that the lobe prescribes an energy cone. The angular position of the lobe in combination with a signal received may be utilized to develop a tracking function in the coordinates about the line axis.

Various procedures have been proposed for achieving this conical scanning eifect. One such procedure involves the tilting of the axis of a rotating reflector about the focal point of the reflector by an amount equal to the scan angle. Another procedure leaves the reflector stationary but moves the radiator or feed through a circular path in a plane passing through the focal point of the reflector and perpendicular to the axis of the reflector. Both of these procedures are satisfactory at low scanning speeds but are mechanically impractical at higher scanning speeds.

A third proposal utilizes a dielectric wedge lens positioned between the radiator or feed and the reflector. The dielectric wedge lens acts to retard the wave front of the signals, the degree of wave front delay being determined by the dielectric constant and the distance traversed. If the dielectric wedge lens is rotated, the phase center of the propagated wave will be emanated in an angular direction as determined by the maximum phase delay introduced by the thick side of the wedge as related to the thin side of the wedge. Although the use of such a rotating dielectric wedge lens reduces in some degree the mechanical difliculties presented, it does not solve them completely as the wedge by its very nature is dynamically unbalanced and therefore its rotation at high speeds often causes damage to its supporting structure. Furthermore, the antenna systems utilizing dielectric wedges so far proposed have suffered from reflection of the energy from the wedge back into the feed, with a consequent reduction in transmission efliciency. It has also been found difficult to provide satisfactory impedance matching for the feed resulting in a further loss in efficiency.

According to the present invention, it has been found that a dielectric wedge lens can be provided that is dynamically stable, greatly reduces the effects of reflected energy, and provides good impedance matching for the feed. Dynamic balance is achieved by providing a second dielectric wedge having substantially the same density as the first wedge but having a higher dielectric constant. By proper positioning of these wedges, reflection of energy back into the feed can be avoided and good impedance matching can be obtained.

It is therefore an object of the present invention to provide a dielectric wedge lens which is dynamically stable.

It is also an object of the present invention to provide a dielectric wedge lens which minimizes the amount of energy reflected back into the feed.

3,255,451 Patented June 7, 1966 It is also an object of the present invention to provide a dielectric wedge lens which is composed of two wedges compounded together.

It is a further object of the present invention to provide a dielectric wedge lens composed of two wedges compounded together in a manner which causes the major reflection from the lens to be directed away from the feed and cancels out a portion of the remainder by destructive superposition.

These and other objects and advantages of the present invention will become more apparent upon reference to the attached description and drawings in which:

FIGURE 1 is a cross sectional side view of the lens of the present invention;

FIGURE 2 illustrates a typical wave trace produced by the lens of the present invention;

FIGURE 3 is a cross sectional side view of a modification of the lens shown in FIGURE 1;

FIGURE 4 is a partial front view of the lens shown in FIGURE 3; and

FIGURE 5 is a cross sectional side view of the dielectric lens of the present invention mounted in a system suitable for conical scanning.

Referring now to FIGURE 1, there is shown a dielectric wedge lens generally indicated at 12 suitable for use in a conical scanning system. This lens consists of a dielectric wedge 14 and a dielectric wedge 16 compounded together. Each of the wedges has an inner curved surface, the centers of curvature of the two surfaces being dispaced from each other so that the wedges have a thick portion and a thinner portion. For the sake of convenience, this type of structure will be referred to in the specification and claims as a wedge. In the preferred embodiment illustrated, each of the wedges has an inner concave hemispherical surface and an outer convex hemispherical surface lying on the same side of a common plane which contains both centers of curvature. As illustrated, these wedges are full hemispheres; a lesser segment of a sphere could also be used and for the sake of convenience all such wedges will be referred to in the specification and claims as hemispherical wedges.

The first wedge 16 has a very low dielectric constant while the second wedge 14 has a relatively higher dielectric constant. The wedges 14 and 16 are preferably made of the same material, such as a low dielectric porous material or plastic foam such as polyester polyurethane. In order to increase the dielectric constant of the wedge 14, an additional material such as barium titanate is mixed into the material forming the wedge 14. Since the material density is approximately the same for each of these wedges 14 and 16, and since the mechanical thickness is now uniform throughout, the compound wedge 12 is dynamically balanced and can be rotated at high speed without producing an excessive gyroscopic efiect and exerting excessive unbalanced forces on its supporting structure.

The provision of two dielectric hemispherical wedges 14 and 16 also minimizes the amount of energy reflected back into the feed. In the prior dielectric lenses having only one hemispherical wedge, the boundary of the wedge towards the feed had a hemispherical shape with the feed phase center being located at the center of the sphere. As a result, the total reflection from the surface of the wedge was concentrated at the feed phase center with consequent impairment of the performance of the feed and an increase in its standing wave ratio. The twowedge construction of FIGURE 1 reduces this problem by making the spherical surface of which the feed phase center is the center of a low dielectric material, with the result that a smaller amount of energy is reflected back into the feed.

Considering the feed phase center to be at the point 18, it can be seen that all of the energy reflected from the boundary of the wedge 16 is reflected back into the feed phase center. As is well known, however, the amplitude of reflection from a surface is determined by the dielectric constant of the material. Thus, the greatest amount of reflection will take place at the boundary between the wedges 16 and 14. As can be seen from FIGURE 1, the center of this spherical surface is a point 20 displaced from the feed phase center 18 and thus the reflection from it will not affect its performance. The point 20 will, of course, prescribe a conic section about the point 18 as the lens is rotated.

Although the wedge thus far described is rotationally balanced, the plastic foam would not be structurally adequate to maintain its geometric shape at high rotational rates. Since any distortion in the shape of the lens would result in the introduction of error into the direction of wave propagation and would result in a change in reflection as seen by the feed, thin fiberglass or resinous structural surfaces 22 and 24 are coated on either side of the lens and serves to prevent distortion of the wedges themselves. The addition of these structural surfaces will, however, constitute an additional boundary at which reflection will occur.

FIGURE 2 shows an approximate ray trace to be expected from a lens constructed as shown in FIGURE 1 and provided with structural surfaces of the type described having a dielectric constant less than that of wedge 14. For the sake of clarity the section of the wedge illustrated is shown to have straight surfaces rather than the hemispherically curved surfaces which they possess in actuality. Also, for the sake of simplicity the reflection at the boundaries between the surface layer 24 and the wedge 16 and the surface layer 22 and the air are disregarded as these reflections are small and can essentially be considered as part of the reflection from the other surfaces of the layers 22 and 24.

As can be seen from FIGURE 2, the three major boundaries where reflection takes place are the boundary between the air and the surface layer 24, the boundary between the wedge 16 and the wedge 14, and the boundary between the wedge 14 and the layer 22. The reflection from these three surfaces are designated as r r and r respectively. As was mentioned before, the amplitude of reflection from a surface is determined by the dielectric constant of the material and thus the reflections r have by far the greatest amplitude. It can be seen, however, that these reflections are directed away from the feed phase center and thus do not affect its performance. The reflections r on the other hand, are collirnated in the feed phase center and thus do affect its performance. The amplitude of these reflections are, however, relatively small. The reflections r are partially directed back into the feed phase center and thus it can be seen that by providing a proper thickness to the lens 12 and by spacing it a proper distance from the feed phase center the reflections r and r may be destructively superimposed, thus reducing their combined effect on the feed phase center.

Due to the varying Wedge thicknesses, electrical symmetry of the lens in the direction of propagation cannot be achieved. If it were possible to achieve electrical symmetry the reflections from the boundaries and feed could be completely cancelled and transmission could be maximized. Such matching to the feed could be accomplished by adjusting the lens thickness and the distance from the feed to the near boundary of the lens so that the reflections from the boundaries and feed are equal in magnitude and 180 out of phase in the direction of the feed. These adjustments may be calculated and made in the same manner as previously used to provide windows or enclosures for wave guides, as will be apparent to one skilled in the art. With the lens configuration shown in FIGURE 1, this condition can only partially be approximated because of the varying eleca trical position of the second boundary relative to the feed due to the varying electrical distance over the area of the wedge media.

Reflection from the lens back into the feed can further be reduced in a manner illustrated by FIGURES 3 and 4. As shown in these figures, the lens may be provided with an array of dielectric cylinders having a lower dielectric constant than that of the containing, or lens, media and an electrical distance of one-quarter of the working wave length. The reflective index of the onequarter wave length cylinders should be the geometric mean between that of air and the lens media. Inasmuch as the electrical distance across the lens 12 varies, the depth of the one-quarter wave length cylinders will also vary across the surface of the lens.

FIGURE 5 shows the compound dielectric lens of the present invention positioned in a system suitable for conical scanning. The lens is positioned a suitable distance from a conventional horn feed 28 and is mounted for rotation about the line axis of the feed on a drive shaft 30 by means of a suitable coupler 32. The drive shaft 30 is rotated by a motor 34 so that the energy refracted by the lens 12 is directed onto the parabolic reflector 36 having its axis lying on the line axis of the feed.

From the foregoing description, it may be seen that a compound dielectric wedge lens has been provided which permits high-speed conical scanning because of its dynamic balance and consequent reduction in gyroscopic action. Gyroscopic action is further reduced because of the decreased weight of the lens resulting from the use of plastic foam in its construction. The transmission properties of the lens are superior to those provided heertofore because the use of two wedges enables the amount of energy reflected into the feed to be significantly reduced.

The invention may be embodied in other specific forms not departing from the spirit or essential characteristics thereof. Th present embodiments are therefore to be considered in all respects as illustrative and not restrictive, th scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

I claim:

1. A dielectric wedge lens, comprising: a first hemispherical wedge of dielectric material, said first wedge having an outer hemispherical surface and an inner hemispherical surface; a second hemispherical wedge of a dielectric material having a higher dielectric constant than said first wedge material, said second wedge having an outer hemispherical surface and an inner hemispherical surface, the inner hemispherical surface of said second wedge having the same radius as the outer hemispherical surface of said first wedge; said first and second wedges being compounded together with said outer hemispherical surface of said first wedge being in contact with the inner surface of said second wedge.

2. A dielectric wedge lens comprising: a first hemispherical wedge of dielectric material, said first wedge having an outer hemispherical surface and an inner hemispherical surface, said surfaces having displaced centers of curvature whereby said wedge has a thick portion and a thinner portion; a second hemispherical wedge of a dielectric material having a higher dielectric constant than said first wedge material, said second wedge having an outer hemispherical surface and an inner hemispherical surface, the inner hemispherical surface of said second wedge having the same radius as the outer hemispherical surface of said first wedge, said surfaces having displaced centers of curvature whereby said wedge has a thick portion and a thinner portion; said first and second wedges being compounded together with said outer hemispherical surface of said first wedge being in contact wth the inner surface of said second wedge, the thinner portion of said first wedg being adjacent the thick portion of said second wedge whereby the mechanical thickness of said lens is substantially uniform.

3. A dielectric wedge len comprising: a first hemispherical Wedge of dielectric material, said first wedge having an outer hemispherical surface and an inner hemispherical surface, said surfaces having displaced centers of curvature whereby said wedge has a thick portion and a thinner portion; a second hemispherical wedge of dielectric material having a higher dielectric constant than said first wedge material; said second wedge having an outer hemispherical surface and an inner hemispherical surface, the inner hemispherical surface of said second wedge having the same radius as the outer hemispherical surface of said first wedge, said surfaces having displaced centers of curvature whereby said wedge has a thick portion and a thinner portion; said first and second wedges being compounded together with said outer hemispherical surface of said first wedge being in cont-act with the inner surface of said second wedge, the thinner portion of said first wedge being adjacent the thick portion of said second wedge; a first thin layer of structural material coated on the inner surface of said first wedge; and a second layer of said structural material coated on the outer surface of said second wedge.

4. The lens of claim 3 wherein said first and second wedges are formed of a foam plastic material.

5. The lens of claim 3 wherein said first and second wedges are formed of the same material, a substance being added to the material of the second wedge to increase its dielectric constant.

6. The lens of claim 3 wherein the inner surface of said lens is provided with an array of cylinders having an electrical depth of one-quarter of a working wave length.

7. An antenna system for use in conical scanning, comprising in combination: a source of electromagnetic energy; a reflector for reflecting said energy; a dielectric wedge lens positioned intermediate said source and said reflector, said lens comprising a first hemispherical wedge of dielectric material, a second hemispherical wedge of a dielectric material having a higher dielectric constant than said first dielectric material, said wedges being compounded together so that the mechanical distance across the lens is substantially uniform but the electrical distance across the lens is non-uniform; and means connected to said lens for rotating it.

8. .An antenna system for use in conical scanning, comprising in combination: a point source of electromagnetic energy; a reflector positioned about said source for reflecting said energy; a dielectric wedge lens positioned intermediate said source and said reflector for directing said energy onto said reflector at an angle with the axis of said reflector, said lens comprising first and second wedges of dielectric material, the material of the second having a higher dielectric constant than that of the first, said wedges being compounded together with the outer surface of said first wedge adjacent the inner surface of said second wedge providing a lens of uniform mechanical thickness but of non-uniform electrical thickness, said lens being positioned so that the center of curvature of the inner surface of the lens is coincident with said point source but the center of curvature of the boundary between the two wedges is displaced from said point source; and means connected to said lens for rotating it about the axis of said reflector.

9. An antenna system for use in conical scanning comprising in combination: a point source of electromagnetic energy; a reflector positioned about said source for reflecting said energy; a dielectric wedge lens positioned intermediate said source and said reflector for directing said energy onto said reflector at an angle with the axis of said reflector, said lens comprising first and second wedges of dielectric material, said second material having a higher dielectric constant than said first material, each of said lenses having an inner hemispherical surface and an outer hemispherical surface, the wedges being compounded together with the outer surface of said first wedge contacting the inner surface of said second wedge whereby said lens has a uniform mechanical thickness but a nonuniform electrical thickness, said lens being positioned so that the center of curvature of said inner surface of said first wedge is coincident with said point source but the center of curvature of said inner surface of said second wedge is displaced from said point source; and means connected to said lens for rotating it about the axis of said reflector.

10. The apparatus of claim 9 wherein the inner and outer surfaces of said lens are coated with a thin layer of structural material having a dielectric constant less than that of said second wedge.

References Cited by the Examiner UNITED STATES PATENTS 2,422,579 6/ 1947 McClellan 343-754 2,571,129 10/1951 Hansen 343-755 2,689,304 9/1954 Lawrence 343-912 2,887,684 5/1959 Dexter et al. 343-753 OTHER REFERENCES The International Dictionary of Physics and Electronics, Second Edition, N.J., D. Van Nostrand Company, Inc., 1961 (page 903, Prism, Rochon, relied on).

HERMAN KARL SAALBACI-I, Primary Examiner.

W. K. TAYLOR, R. D. COHN, Assistant Examiners. 

1. A DIELECTRICAL WEDGE LENS, COMPRISING: A FIRST HEMISPHERICAL WEDGE OF DIELECTRIC MATERIAL, SAID FIRST WEDGE HAVING AN OUTER HEMISPHERICAL SURFACE AND AN INNER HEMISPHERICAL SURFACE; A SECOND HEMISPHERICAL WEDGE OF A DIELECTRIC MATERIAL HAVING A HIGHER DIELECTRIC CONSTANT THAN SAID FIRST WEDGE MATERIAL, SAID SECOND WEDGE HAVING AN OUTER HEMISPHERICAL SURFACE AND AN INNER HEMISPHERICAL SURFACE, THE INNER HEMISPHERICAL SURFACE OF SAID SECOND WEDGE HAVING THE SAME RADIUS AS THE OUTER HEMISPHERICAL SURFACE OF SAID FIRST WEDGE; SAID FIRST AND SECOND WEDGES BEING COMPOUNDED TOGETHER WITH SAID OUTER HEMISPHERICAL SURFACE OF SAID FIRST WEDGE BEING IN CONTACT WITH THE INNER SURFACE OF SAID SECOND WEDGE. 